Improve tests for legacy script patches.

Context

This is a follow-up from !3730 (comment 868036266). It refactors tests written for legacy contract patches so that they can:

• exist peacefully when nothing is patched (i.e. most of the time);
• be easily adapted to test new patches;
• be easily disabled when they're not needed anymore (deleting just one line is sufficient).

The test module is turned into a functor, so adding new contract patches to tests is simply a matter of applying that functor. On top of that a test is added which type checks the patched contracts without legacy mode.

Manually testing the MR

$ cd src/proto_alpha/lib_protocol/test/integration/michelson && dune exec ./main.exe -- test 'patched contracts'

Checklist

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